Method and apparatus for producing liquid carbon dioxide

ABSTRACT

The invention relates to an apparatus for producing carbon dioxide-rich liquid, which includes a separation unit including a column for physically washing with a solvent and means for cooling a fluid of the separation unit, and a unit for compressing and liquefying a carbon dioxide-rich gas derived from the separation unit, including means for cooling the gas upstream and/or downstream from the compression operation, a single refrigerating cycle using carbon dioxide as the refrigerant, which is suitable for providing frigories to the means for cooling the fluid of the separation unit and to the means for cooling the gas upstream and/or downstream from the compression operation, and means for sending a portion of the liquid from the liquefaction unit to the refrigerating cycle.

The present invention relates to a method and an apparatus for producing a carbon dioxide-rich liquid. It applies in particular to gas separation and purification processes based on the principle of physical absorption, which require operation at temperatures below 0° C., such as the Rectisol® or the Selexol® process, in which the carbon dioxide must be produced either in liquid form, or in compressed form for purposes such as sequestration, EOR (Enhanced Oil Recovery), or any other application dedicated to reducing carbon dioxide emissions.

In a gas separation and purification unit based on the physical absorption principle which requires operation at temperatures below 0° C., like the Rectisol® or the Selexol® process, it is necessary to supply large refrigeration loads for the process to operate efficiently, The refrigeration duty is commonly supplied by refrigerating units operating on fluids external to the process, such as ammonia or propylene, for example.

In the context of reducing carbon dioxide emissions by precombustion processes, the separated carbon dioxide must be produced either in liquid form for road, river or maritime transport, or in compressed form for pipeline transport. These processes also use a compressor operating with the fluid to be liquefied (carbon dioxide) to provide the heat balance required for producing carbon dioxide in liquid or compressed form.

FIG. 1 shows an apparatus of the prior art. A gas separation and purification unit of the Rectisol® type 10 separates a gas to be treated containing carbon dioxide 1 to produce a purified gas 2 and a carbon dioxide-rich gas. The separation unit 10 is cooled by means of an external refrigerating unit 11 using a refrigerant 3, 3′, The carbon dioxide is liquefied in a liquefier 12 to produce liquid carbon dioxide 5.

According to an object of the invention, a method is provided for producing a carbon dioxide-rich liquid as end product, in which:

i) a feed gas comprising carbon dioxide is separated by physical washing with a solvent at a temperature below 0° C.

ii) the solvent required for the physical washing of step i) is cooled

iii) a carbon dioxide-rich gas is produced by separation according to step i), the said gas is compressed and liquefied

iv) the carbon dioxide-rich gas is cooled upstream and/or downstream of the compression operation of step iii) and

v) a single refrigeration cycle, using carbon dioxide as refrigerant, supplies the refrigeration for the cooling operation of step iv) and for a cooling operation required in step i), at least part of the carbon dioxide used as refrigerant issuing from the liquefaction operation of step iii).

According to other optional aspects:

-   -   the same refrigeration cycle serves to cool the carbon         dioxide-rich gas upstream and/or downstream of the compression         operation;     -   the same refrigeration cycle serves to cool the solvent upstream         of the washing operation;     -   the solvent is methanol;     -   the carbon dioxide-rich gas is liquefied after the compression         operation of step iii).

According to a further object of the invention, an apparatus is provided for producing a carbon dioxide-rich liquid as end product, comprising

i) a separation unit comprising a column for physical washing with a solvent and means for cooling a fluid of the separation unit,

ii) a unit for compressing and liquefying a carbon dioxide-rich gas derived from the separation unit in order to produce liquid carbon dioxide as end product, the compression and liquefaction unit comprising means for cooling the gas upstream and/or downstream of the compression operation,

iii) a single refrigeration cycle using carbon dioxide as refrigerant, being suitable for supplying refrigeration to the means for cooling the fluid of the separation unit and to the means for cooling the carbon dioxide-rich gas upstream and/or downstream of the compression operation and

iv) means for sending part of the liquid carbon dioxide from the separation and liquefaction unit to the refrigeration cycle.

Optionally, the apparatus comprises means for cooling the solvent upstream of the washing operation by means of the refrigeration cycle.

The invention consists in using a single refrigeration cycle supplying the refrigeration for cooling required for the gas separation and purification unit, for example of the Rectisol® type, in particular for cooling the washing solvent, and for cooling a stream of carbon dioxide-rich gas issuing from the gas separation and purification unit.

Such a method serves to reduce the investment by combining the functions. The invention is described in greater detail with reference to FIG. 2.

A unit for separating and purifying gas by physical washing with a solvent at a temperature below 0° C. of the Rectisol® type 10 separates a gas to be treated 1 containing carbon dioxide to produce a purified gas 2 and a carbon dioxide-rich gas 4. The separation unit 10 is cooled by means of a cycle using a refrigerant 103, 103 issuing from a unit 12 for treating the carbon dioxide-rich gas 4. The carbon dioxide treatment unit 12 is a compression unit C followed by a liquefaction unit L producing carbon dioxide in liquid form 5. The carbon dioxide-rich gas compressed by the compression unit C is liquefied by the unit L to produce the end product 5. A portion 103 of the liquid formed can cod the compressed stream downstream and/or upstream of the compression unit C by means of the heat exchangers E1, E2.

In particular, the refrigerant 103 sent to the unit 10 can serve to cod a stream of solvent used in a washing step of the method.

The same fluid can serve to cod the carbon dioxide upstream and/or downstream of the compression operation in the unit 12.

The fluid is carbon dioxide and issues from the gas 4 treated in the unit 12. 

1-10. (canceled)
 11. A method for producing a carbon dioxide-rich liquid as end product, comprising; i) separating a feed gas comprising carbon dioxide by physical washing with a solvent at a temperature below 0° C., ii) cooling the solvent required for the physical washing of step i), iii) producing a carbon dioxide-rich gas by separation according to step i), said gas is compressed and liquefied, iv) cooling the carbon dioxide-rich gas upstream and/or downstream of the compression operation of step iii) and, v) supplying the refrigeration for the cooling operation of step iv) and for a cooling operation required in step I) with a single refrigeration cycle, using carbon dioxide as refrigerant, at least part of the carbon dioxide used as refrigerant issuing from the liquefaction operation of step iii).
 12. The method of claim 11, further comprising cooling the solvent upstream of the washing operation with said refrigeration cycle.
 13. The method of claim 11, wherein the solvent is methanol.
 14. The method of claim 11, wherein the carbon dioxide-rich gas is liquefied after the compression operation of step iii).
 15. The method of claim 11, wherein the carbon dioxide-rich gas is cooled upstream of the compression operation of step iii) by means of the refrigeration cycle.
 16. The method of claim 11, wherein the carbon dioxide-rich gas is cooled downstream of the compression operation of step iii) by means of the refrigeration cycle.
 17. An apparatus for producing a carbon dioxide-rich liquid as end product, comprising i) a separation unit comprising a column for physical washing with a solvent and means for cooling a fluid of the separation unit, ii) a unit for compressing and liquefying a carbon dioxide-rich gas derived from the separation unit, the compression and liquefaction unit comprising means for cooling the carbon dioxide-rich gas upstream and/or downstream of the compression operation, iii) a single refrigeration cycle using carbon dioxide as refrigerant, being suitable for supplying refrigeration to the means for cooling the fluid of the separation unit and to the means for cooling the carbon dioxide-rich gas upstream and/or downstream of the compression operation and iv) means for sending part of the carbon dioxide-rich liquid from the separation and liquefaction unit to the refrigeration cycle.
 18. The apparatus of claim 17, wherein the refrigeration cycle is suitable for supplying refrigeration upstream of the compression of the carbon dioxide-rich gas.
 19. The apparatus of claim 17 the compression of the carbon dioxide-rich gas.
 20. The apparatus of claim 17, comprising a means for cooling the solvent upstream of the washing operation by means of the refrigeration cycle. 